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Nanoparticles have been reported to induce toxicity to aquatic organisms, however, their potential impacts on phosphorus removal from wastewater by algae are unclear. In this study, the effects of nanoparticle ZnO (nano-ZnO) on phosphate (PO 4 3− ) removal by a green alga Chlorella vulgaris were investigated. We found that PO 4 3− removal efficiency was accelerated with high concentrations of nano-ZnO (0.04–0.15 mM) but reduced with low concentrations of nano-ZnO (0.005–0.04 mM) compared to the control (without nano-ZnO), suggesting that PO 4 3− removal efficiency by C. vulgaris was related to nano-ZnO concentrations. Moreover, we observed changes of nano-ZnO morphology and detected element P on the surface of nano-ZnO by using transmission electronic microscopy (TEM) combined with energy dispersive X-ray spectroscopy (EDX), indicating that PO 4 3− was interacted with nano-ZnO or the dissolved Zn 2+ from nano-ZnO. Furthermore, we confirmed this interaction induced the formation of Zn 3 (PO 4 ) 2 crystallites sedimentation by employing X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS), which finally accelerates the removal of PO 4 3− . [ABSTRACT FROM AUTHOR]

Abstract This study investigated the influences of cetyltrimethyl trimethyl ammonium chloride (CTAC), an emerging pollutant quaternary ammonium compound (QAC) in municipal effluents, on the transfer and uptake of NH 4 + by Chlorella vulgaris F1068 cells removed EPS artificially (EPS-R) and coated EPS naturally (EPS-C) under different scenarios (e.g., the presence or absence of CTAC, different photoperiod sequences (light 12 h: dark 12 h or dark 12 h: light 12 h)). The results showed that the removal of EPS increased the transfer and uptake of NH 4 + but the presence of EPS caged NH 4 + and effectively weakened the stress of CTAC (<0.5 mg/L) on NH 4 + uptake. The main mechanism was considered that CTAC in the concentration range from 0.1 to 0.5 mg/L induced an increased amount of polysaccharide and protein in EPS and thus protected algal normal physiological functions (including cell membrane permeability and glutamine synthetase activity) from the damage of CTAC (0.1 to 0.5 mg/L) regardless of the photoperiod sequences. Thereby, the findings of this study provided an insight into the role of algal EPS in transfer and uptake of nutrients under the coexisted toxics for the future algae-based sewage treatment application. Graphical abstract Unlabelled Image Highlights • CTAC decreased uptake of NH 4 + but EPS retarded the decline of NH 4 + uptake. • EPS of algae F1068 decreased the toxicity of CTAC (<0.5 mg/L). • CTAC (<0.5 mg/L) increased the contents of polysaccharide and protein in EPS. • EPS protected algal membrane permeability, fluidity and glutamine synthetase. • EPS removal increased influx and uptake of NH 4 + compared to the presence of EPS. [ABSTRACT FROM AUTHOR]